1. Field of the Invention
The present invention relates to an organic light emitting diode (OLED) display. More particularly, the present invention relates to an OLED which can maximize a contact area of a common voltage contact portion of a common voltage line and minimize a voltage drop of a driving voltage line while reducing a dead space.
2. Description of the Related Art
An organic light emitting diode (OLED) display includes two electrodes and an organic emission layer disposed between the two electrodes, and electrons injected from one electrode and holes injected from the other electrode are combined in the organic emission layer such that excitons are formed, and light is emitted by energy generated from the excitons.
The OLED display has self-luminance characteristics, and unlike a liquid crystal display (LCD), the thickness and weight thereof can be reduced since a separate light source is not required. Furthermore, since the organic light emitting diode display has high quality characteristics such as lower power consumption, high luminance, and short response time, it has been spotlighted as a next generation display device.
A unit pixel of such an OLED display includes a switching transistor, a driving transistor, a capacitor, and an organic light emitting diode (OLED), and the driving transistor and the capacitor are provided with a driving voltage Vdd from a driving voltage line, and the driving voltage line controls a current flowing to the organic light emitting diode through the driving transistor. In addition, a common voltage line connected to a cathode supplies a common voltage Vss to the cathode so as to make a current flow by forming a voltage potential difference between a source and drain and the cathode.
The driving voltage line and the common voltage line receive a driving voltage and a common voltage, respectively, from an external source through a driving voltage pad and a common voltage pad, respectively, formed in a periphery portion formed at the periphery region of a pixel portion where a plurality of pixels are formed. However, as the area of the driving voltage line and the common voltage line is increased in the periphery portion, the area of the pixel portion is reduced, and the area of the driving voltage line and the common voltage line mostly become a dead space where no pixel portion is formed, and thus no image can be displayed.
When the width of the common voltage line is reduced in order to reduce the dead space, the contact area of the common voltage contact portion is reduced so that current density is increased, thereby causing a heat generation problem.
Furthermore, when the width of the driving voltage line is reduced to reduce the dead space, the current density and luminance non-uniformity drop (IR DROP) due to a severe voltage.
The above information disclosed in this Background section is only for enhancement of an understanding of the background of the invention, and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.